DIFFUSION OF LINEAR POLYSTYRENE INTO CROSS-LINKED POLYSTYRENE

The diffusion of linear polystyrene (PS) into its crosslinked counterp art was studied using both neutron reflectivity (NR) and forward recoi l scattering (FRES). The penetrant molecular weights were monodisperse and ranged from 10000 to 690000 gmol(-1). The molecular weight betwee n crosslinks was kept at 22000 g mol(-1). The crosslinks were introduc ed by polymerizing styrene monomer in the presence of divinylbenzene. The FRES results revealed the presence of a high molecular weight cut- off for the linear PS above which diffusion could not proceed. The NR results indicated that even at these high molecular weights a certain amount of diffusion did occur but was confined to the first few hundre d Angstroms of the interface. A step function in the polymer concentra tion profile was found at these high molecular weights as expected for systems showing a limited solubility for the diffusant. The counter d iffusion of residual sol from the crosslinked network is used to expla in certain features of the diffusion profile. (C) 1997 Elsevier Scienc e Ltd.